In many medical procedures, various physiological conditions present within a body cavity need to be monitored. These physiological conditions are typically physical in nature—such as pressure, temperature, rate-of-fluid flow, and provide the physician or medical technician with critical information as to the status of a patient's condition.
One device that is widely used to monitor conditions is the blood pressure sensor. A blood pressure sensor senses the magnitude of a patient's blood pressure, and converts it into a representative electrical signal that is transmitted to the exterior of the patient.
For most applications it is required that the sensor is electrically energized. Some means of signal and energy transmission is thus required, and most commonly extremely thin electrical cables, sometimes called microcables, are provided inside a guide wire, which itself is provided in the form of a tube, which often has an outer diameter in the order of 0.35 mm, and oftentimes is made of steel.
In order to increase the bending strength of the tubular guide wire, a core wire is positioned inside the tube. The core wire also helps to improve “pushability” and “torquability” of the guide wire. The mentioned electrical cables are e.g. positioned in the space between the inner lumen wall and the core wire.
Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, typically a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon.
As is disclosed in, for example, U.S. Pat. No. 6,167,763, which also is assigned to the present assignee, the sensor element can be arranged inside a short tube (usually referred to as a sleeve or jacket), which protects the sensor element and comprises an aperture through which the pressure sensitive device is in contact with the ambient medium. The U.S. Pat. No. 6,167,763 further illustrates that a first coil may be attached to the distal end of the jacket and that a similar second coil may be attached to the proximal end of the jacket. The solid metal wire—which, as also mentioned above, in the art usually is referred to as the core wire—extends through the interior of the jacket and may be provided with an enlarged diameter portion adapted for mounting of the sensor element.
In WO 2009/054800 A1, assigned to the present assignee, another example of a sensor guide wire for intravascular measurements of physiological variables in a living body, is disclosed. The sensor guide wire has a proximal shaft region, a flexible region and a distal sensor region. In one embodiment sensor guide wire is provided with a tip wire comprising a tip core wire.
It is advantageous if the sensor guide wire tip is flexible in order to make the various bends and turns that are necessary to navigate through the tortuous vessels, e.g. when navigating the sensor guide wire through coronary arteries. In sensor guide wires according to the Prior Art, as disclosed in for example the above mentioned U.S. Pat. Re. 35,648, the distal tip portion of the sensor guide wire is often made more flexible by grinding the core wire to a smaller dimension. Oftentimes, as also disclosed in U.S. Pat. Re. 35,648, the core wire is flattened in order to make the tip more flexible. A flattened core wire tip is mainly flexible in two directions.
This is also illustrated by e.g. US 2007/0255145, which discloses a sensor guide wire, provided with a core wire which is flattened at the tip of the sensor guide wire.
Besides from being flexible enough, it is also important that the sensor guide wire tip responds when steering the sensor guide wire through the tortuous vessels, i.e. the sensor guide wire tip must also have sufficient “steering response”. “Steering response” is a measure of the irregular behavior of a sensor guide wire when the sensor guide wire tip is subjected to a non-linear pathway and rotated. The “steering response” of a sensor guide wire tip is a general property of the distal tip components.
The present inventors have identified some situations when applying the sensor guide wire in tortuous vessels where improved properties regarding flexibility, pull strength and steering response of the sensor guide wire tip would be advantageous.
An object of the present invention is therefore to provide an improved sensor guide wire comprising an improved tip, with sufficient pull strength and which tip is flexible in all directions, and which also is improved regarding the capability of being steered through the various bends and turns in the vessels.